The invention relates to a treatment device for treating food products with conditioned air, comprising a housing, at least one conveyor means for conveying the products through the housing along a helical conveying path, air-circulation means for causing a flow of air to flow through the housing, as well as air-conditioning means for conditioning the flow of air.
A treatment device of this nature, in the form of a climate chamber, is known from EP-B-0 333 565. This known device comprises a housing containing a helical conveyor belt which can move around the axis of the spiral, means for causing a conditioned gas or vapour to circulate inside the housing and around each product which is situated on the conveyor belt, first and second support means being provided in order to support the inner and outer edges, respectively, of the conveyor belt. In an embodiment of this known device, a circulation of air is generated in the housing, with conditioned air being blown onto the conveyor belt from the entire circumference of the drum around which the conveyor belt is moving, which conditioned air is then sucked in next to the conveyor belt and, following conditioning in the air-conditioning means, is blown back into the drum. In another embodiment of this device, the air is directed, by means of suitable baffle plates, towards a limited air-inlet area on the outside of a helical conveyor, from where the air flows horizontally over the conveyor belt, and the air is split into two and is removed on the other side opposite the air-inlet area. In further embodimentsxe2x80x94aiming to reduce the pressure drop across the device and to improve the heat transfer xe2x80x94the air, after it has been guided over the conveyor belt, leaves the helical conveyor at one or both of its axial ends. In this case, the air may be guided over the products either from the inside or from the outside of the conveyor belt, after which the air flows through the turns of the conveyor belt towards one or both axial ends.
It should be noted that in this description (helical) conveyor is understood to mean the assembly of a central column or shaft and the conveyor means which is guided around it along a helical path, as well as the associated support means for supporting the conveyor means.
Furthermore, EP-A-0 804 878 has disclosed a furnace for preparing food products which comprises a housing as well as a helical conveyor which is disposed therein and on which the food products can be accomodated, as well as heating means and so-called xe2x80x9cboosterxe2x80x9d means for generating a flow of hot air through the housing with a view to heating the food products which lie on the belt. In this housing, guide means for guiding the flow of hot air over the conveyor belt are disposed in such a manner that the products are heated uniformly in the transverse direction of the belt. According to the embodiment described in this European Patent application, air is blown onto the food products on the conveyor belt from the outside. A number of features are provided for guiding and directing the flow of hot air, which features are disposed on the outside of the helical conveyor and between the turns of the latter.
One of the drawbacks of this known device is that the conditioned air flows along the inside of the wall of the housing of the oven, which wall forms a large heat-exchanging surface with the environment, resulting in the loss of energy before the flow of hot air is directed onto the products in order to subject them to a temperature treatment. A further drawback is that the hot air is guided over the products from the outside of the conveyor belt, where the product density on the conveyor belt is less than on the inside of the conveyor belt, so that the highest intensity of heat is available at a location where there is no need for this intensity to be so high. It is thus impossible for a uniform temperature treatment to take place. The guide means, which extend between the turns, in addition give rise to an accumulation of contamination, such as fat and the like in the case of meat products, for example, which cannot easily be removed owing to the limited accessibility of the helical conveyor which is caused by these guide means being present between the turns. Also, the presence of the guide means on the outside of the helical conveyor interferes with a compact structure of the device. Furthermore, two so-called xe2x80x9cbooster meansxe2x80x9d per spiral are required to obtain any form of controlled air flow. The devices known to date are designed in such a way as to subject all types of products to a temperature treatment which is virtually identical for each type of product, possibly designed with different compartments for different temperatures. However, each type of product requires specific preparation conditions, such as time-dependent temperature, air flow and moisture conditions, which are connected with the microstructure of the product type. For example, the heating of the inside of a product in order to bring about the desired change in proteins and flavourings is different for each type of product. For example, a fatty product transmits temperature from its outside to its inside differently from a product with little fat. Consequently, different treatments would be required for optimum preparation of different types of products. The shape of a product also plays a role in this context. However, in practice, the starting point is average conditions for all types of product together, so that it is not possible to achieve optimum preparation which is oriented to a specific type of product.
One object of the present invention is to provide a treatment device for treating food products, in particular meat products with conditioned air, which device does not present the abovementioned drawbacks, or presents them to a lesser extent.
More particularly, one object of the invention is to provide a device of this nature in which conditioned air is brought into contact with the products to be treated in a controlled manner in order to create conditions which are adapted to the product.
A further object of the invention is to provide a device of this nature in which energy loss to the environment is considerably reduced.
Yet another object is to reduce environmental pollution caused by the device.
A further object of the invention is to provide a device of this nature which is easily accessible for cleaning and/or maintenance work, while the device still has a compact structure and thus takes up little space.
A further object of the invention is to provide a device in which various preparation methods can be combined, in particular a treatment device in which a treatment with steam is followed by a different preparation method, such as cooking or grilling.
The treatment device according to the invention of the type mentioned above is, to this end, characterized in that air-distribution means for distributing the flow of air via only part of the inside of the helical conveying path are disposed on the inside of the helical conveying path, which air-distribution means are connected to the said air-circulation means.
In the device according to the invention, conditioned air is fed to air-distribution means which are disposed in the helical column and which are designed to distribute the flow of conditioned air over the turns of the helical conveyor via a limited inlet area. Blowing the air in centrally via the air-distribution means reduces the energy losses, since the heat is transferred directly to the products which are to be treated. Furthermore, the product density on the conveyor belt directly adjacent to the central column is greater than on the outer edge, so that blowing hot air onto the products on the inside provides the highest energy intensity at the location where this is required. In order to enable the treatment conditions for each product to be as uniform as possible, the air is made to flow out over the turns of the helical conveyor from only a part of the inside of the helical conveying path. The air which has been distributed into layers then flows partially in cocurrent and partially in countercurrent over the turns of the helical conveyor. The nature of the conveyor belt is such that the flow of air through the belt is relatively low compared to the flow of air which passes over the belt in cocurrent and countercurrent. This directed flow is, in addition to the only partially open air-distribution means, also controlled by the air-circulation means which suck the air in and then send it to the air-conditioning means. The layered distribution makes it possible to control the conditions around each product at any desired time and any desired location, so that a product-specific treatment can be carried out. In principle, the intensity, i.e. volume, velocity and/or the temperature of the conditioned air can be controlled for each turn.
It should be noted that in the present application, the term conditioned air is understood to mean air whose temperature and/or moisture content and/or velocity/volume is controlled. A high air velocity or air volume in combination with a high temperature provides the possibility of rapidly searing the surface of a product. Furthermore, the temperature is important for cooking products, while the air humidity is important in connection with products being dried out in a warm environment. Air to which steam is added may also be used as the treatment medium. In this case, the air-conditioning means comprise, for example, one or more steam nozzles which are connected to a steam generator or the like. Treatment processes in which these parameters play a role include, inter alia, cooking, precooking, steaming, grilling and baking/frying of food products, in particular meat products, which are prepared ready to eat. Other processes include drying, cooling and freezing.
The treatment device can be controlled using fuzzy logic, in order for it to be possible to carry out. the treatment in the optimum possible way with regard to specific product preparation conditions and energy loss.
With a view to further reducing the energy loss, the housing may be in the form of a cylinder which substantially corresponds to the outer circumference of the helical conveyor.